U.S. patent application number 11/895647 was filed with the patent office on 2008-02-28 for method for contact-free testing of antennas applied to a material web.
Invention is credited to Michael Kohla.
Application Number | 20080048670 11/895647 |
Document ID | / |
Family ID | 38564744 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080048670 |
Kind Code |
A1 |
Kohla; Michael |
February 28, 2008 |
Method for contact-free testing of antennas applied to a material
web
Abstract
A method for contact-free testing of antennas applied to a
material web, wherein the material web having the antennas is
passed to a measurement device. The antennas are passed past an
assigned measurement antenna arrangement of the measurement device
in the region of the measurement device and the measurement antenna
arrangement has a high-frequency signal S.sub.mess of a transmitter
applied to it. This signal is correlated with a pre-determined
working frequency f.sub.A of the antennas. The high-frequency
signal S.sub.ruck that returns from the measurement antenna
arrangement is determined and compared with default values, and the
adherence to production tolerances is determined by the comparison
of the returning high-frequency signal S.sub.ruck with the default
values for each of the individual antennas.
Inventors: |
Kohla; Michael; (Havixbeck,
DE) |
Correspondence
Address: |
WILLIAM COLLARD;COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
38564744 |
Appl. No.: |
11/895647 |
Filed: |
August 24, 2007 |
Current U.S.
Class: |
324/537 |
Current CPC
Class: |
G06K 19/0722 20130101;
G01R 31/2822 20130101; H01Q 1/2208 20130101; G01R 31/013 20130101;
G01R 29/10 20130101 |
Class at
Publication: |
324/537 |
International
Class: |
G01R 31/01 20060101
G01R031/01 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2006 |
DE |
10 2006 040 180.8 |
Claims
1. A method for contact-free testing of antennas for RFID chips,
said antennas being applied to a material web and having at least
one conductive track and non-contacted connector ends, the method
comprising the following steps: passing the material web to a
measurement device so that the antennas each are passed past an
assigned measurement antenna arrangement of the measurement device;
applying a high-frequency signal S.sub.mess of a transmitter to the
measurement antenna arrangement, which signal is correlated with a
pre-determined working frequency f.sub.A of the antennas;
determining a high-frequency signal S.sub.ruck that returns from
the measurement antenna arrangement; comparing said high-frequency
signal with default values; and determining adherence to production
tolerances for each antenna by means of said step of comparing.
2. A method according to claim 1, wherein the high-frequency signal
S.sub.mess is passed from the transmitter to the measurement
antenna arrangement by way of a directional coupler that emits a
first measurement signal that is proportional to high-frequency
power P.sub.vor which runs to the measurement antenna arrangement,
and wherein the directional coupler emits a second measurement
signal that is proportional to high-frequency power P.sub.ruck
which is reflected by the measurement antenna arrangement.
3. A method according to claim 1, wherein the measurement antenna
arrangement has a high-frequency signal S.sub.mess applied to it, a
frequency f.sub.mess of which approximately corresponds to twice a
working frequency f.sub.A.
4. A method according to claim 1, wherein the measurement antenna
arrangement has a high-frequency signal S.sub.mess applied to it, a
frequency f.sub.mess of which approximately corresponds to a
working frequency f.sub.A.
5. A method according to claim 1, wherein the material web is
passed past the measurement device at an average web speed of more
than 0.8 m/s.
6. A method according to claim 1, wherein at least 50 measurement
values of the returning high-frequency signal S.sub.ruck are
determined for each of the antennas, and subsequently averaged.
7. A method according to claim 1, wherein the antennas that do not
meet the production tolerances are marked or removed.
8. A method according to claim 1, wherein the measurement antenna
arrangement has a high-frequency signal S.sub.mess in the UHF band
applied to it by the transmitter.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a method for contact-free testing
of antennas for RFID labels applied to a material web. RFID labels
have not only an antenna but also an RFID chip as an active or
passive circuit, and are suitable, for example, for identifying
objects of all kinds, such as goods and transport packagings. In
the identification of the packaging of mass-produced articles, in
particular, only one-time use of an RFID label is generally
provided, so that production costs are particularly low.
[0003] 2. The Prior Art
[0004] U.S. Pat. No. 6,147,662 describes a method for the
production of RFID labels, wherein an antenna is imprinted onto a
material web with conductive ink or with conductive toner, and
wherein subsequently, an RFID chip is set onto the antenna and
contacted with it. The RFID labels are passed to a measurement
device before being wound up into a roll, with defective RFID
labels being determined and marked. In the case of RFID labels that
are operated at a frequency in the UHF range (300 MHz to 3000 MHZ),
in particular, a high level of rejects must be expected because the
structures are usually fine. The production costs are greatly
increased by a high level of rejects, since the entire RFID labels,
with their antenna and RFID chip, must be sorted out and disposed
of.
SUMMARY OF THE INVENTION
[0005] With this background, it is an object of the invention to
reduce the costs of the production of RFID labels.
[0006] This object is accomplished, according to the invention, by
means of a method for contact-free testing of antennas for RFID
chips applied to a material web, wherein the material web having a
plurality of antennas, which each have at least one conductive
track and non-contacted connector ends, is passed to a measurement
device. The antennas are each passed past an assigned measurement
antenna arrangement of the measurement device in the region of the
measurement device. The measurement antenna arrangement has a
high-frequency signal S.sub.mess of a transmitter applied to it,
which signal is correlated with a pre-determined working frequency
f.sub.A of the antenna. The high-frequency signal S.sub.ruck that
returns from the measurement antenna arrangement is determined and
compared with default values, and the adherence to production
tolerances is determined by means of the comparison of the
returning high-frequency signal S.sub.ruck with the default values
for the individual antennas, in each instance. According to the
invention, checking of the antennas takes place before these are
contacted with an RFID chip, and defective antennas, which must be
sorted out, are not provided with an RFID chip. Furthermore, an
increase in the reject rate can be detected directly, even during
the production of antennas for RFID labels, and the production
process can then be adjusted or interrupted.
[0007] The method according to the invention is particularly
suitable for antennas whose working frequency lies in the UHF
range, since in the case of these antennas, an increased level of
rejects must be expected, because of the fine structures. This is
particularly the case for mass production using a printing method,
for example an intaglio printing method.
[0008] According to the invention, the measurement antenna
arrangement of the measurement device has a high-frequency signal
of the transmitter applied to it, and part of the high-frequency
power is emitted by the measurement antenna arrangement and
absorbed by the antenna to be tested. In this connection, it is
practical to select the frequency f.sub.mess of the transmitter in
such a manner that the antennas to be tested, which lie within
pre-determined production tolerances, absorb a maximum of the
high-frequency power, thereby also minimizing the high-frequency
signal S.sub.ruck that returns to the connector of the measurement
antenna arrangement. In order to determine the power that is
assigned to the outgoing high-frequency signal S.sub.mess, and the
power assigned to the returning high-frequency signal S.sub.ruck,
the high-frequency signal S.sub.mess is preferably passed from the
transmitter to the measurement antenna arrangement by way of a
directional coupler that emits a first measurement signal that is
proportional to the high-frequency power P.sub.vor, which runs to
the measurement antenna arrangement. The directional coupler emits
a second measurement signal that is proportional to the
high-frequency power P.sub.ruck, which is reflected by the
measurement antenna arrangement. In practice, the ratio of the
power fed in at the transmitter to the power reflected back by the
measurement arrangement is also indicated in decibels (dB), as the
front-to-back ratio.
[0009] The method according to the invention is fundamentally
applicable to any desired antenna structures. It is practical if
the measurement antenna arrangement is adapted, in terms of its
geometry, to the antennas to be tested. The method according to the
invention is particularly suitable for testing antennas that are
formed as dipole antennas, of two conductive tracks, each having
one connector end. Proceeding from the central connector ends, the
conductive tracks, which have approximately the same length, extend
away from one another. In this connection, the working frequency
f.sub.A of the antenna is determined by means of its total length,
which corresponds to approximately half the wavelength. For testing
these dipole antennas, a separate measurement antenna of the
measurement antenna arrangement is preferably provided for each of
the conductive tracks, and the measurement antenna arrangement has
a high-frequency signal S.sub.mess applied to it, the frequency
f.sub.mess of which approximately corresponds to twice the working
frequency f.sub.A. In this connection, the frequency f.sub.mess
approximately corresponds to twice the resonance frequency that is
to be expected for the individual conductive tracks, in each
instance. If the conductive track does not have any defects, for
example in the form of interruptions, a maximum of energy is
withdrawn from the measurement antenna due to the resonance, and
therefore the high-frequency signal S.sub.ruck that returns from
the measurement antenna on the connector line is also reduced. In
the case of a defective conductive track, there is no resonance
present at the frequency f.sub.mess, so that the proportion of the
returning high-frequency power P.sub.ruck is comparatively great.
In this connection, the adherence to manufacturer tolerances can be
determined for each individual antenna, from the front-to-back
ratio, by determining the returning high-frequency signal
S.sub.ruck, for example by means of a directional coupler and by
means of a subsequent amplifier/evaluation logic. In order to
determine possible short-circuits in the region of the connector
ends, the pre-determined working frequency f.sub.A is applied to
the measurement antenna arrangement according to the same
measurement principle. In the case of a short-circuit, there is a
great increase in the reflected high-frequency power, as compared
with an antenna that is capable of functioning.
[0010] If the antenna has only one conductive track, which can be
formed into a conductor loop, for example, the antenna usually has
one measurement antenna of the measurement antenna arrangement
assigned to it, to which a high-frequency signal S.sub.mess is
applied, the frequency f.sub.mess of which approximately
corresponds to the working frequency f.sub.A to be expected. As
described above, in the case of a defective antenna, in comparison
with an antenna that is capable of functioning, a great increase in
the returning power is observed.
[0011] Due to the contact-free testing of the antennas, a very
great through-put can be achieved. Thus, in a preferred embodiment
of the invention, the material web is passed past the measurement
device at an average web speed of more than 0.8 m/s, preferably
more than 1.6 m/s. In this connection, the individual antennas can
be passed past the measurement antenna arrangement of the
measurement device at a constant web speed, or at a web speed that
is modulated by means of a register roller arrangement, for
example, without any restrictions.
[0012] In a preferred embodiment of the method according to the
invention, at least 50, preferably at least 100 measurement values
of the returning high-frequency signal S.sub.ruck are determined
for each of the antennas, and subsequently averaged. In addition or
alternatively, however, it is also possible to smooth and/or
average the signal directly, by means of a corresponding
configuration of the electrical measurement circuit, for example by
means of filters.
[0013] The antennas found to be defective can be directly removed
from the material web, within the framework of the invention, or,
for example, can be marked by an imprint or a punching.
Furthermore, it is also possible to store the position of defective
antennas on the material web electronically, in the memory of a
control. Subsequently, only antennas capable of functioning are
subsequently provided with an RFID chip, on the basis of this
information.
[0014] Before the contact-free testing takes place, the antennas
are imprinted onto the material web, preferably using a printing
process, for example an intaglio printing process, using conductive
ink. Possible web material is, in particular, polymer film
material, preferably from the group of the polyesters, polyamides,
and polyolefins. The material web typically has a layer thickness
between 30 and 150 .mu.m.
[0015] In particular, in order to allow cost-advantageous
production of the antennas for RFID labels, the material web
preferably has at least two rows of antennas crosswise to its
running direction, with at least one measurement antenna
arrangement of the measurement device provided for each row. In
order to prevent mutual interference of the measurement antenna
arrangements with regard to one another, these are disposed offset
relative to one another in the running direction of the material
web. In this connection, it is practical if the distance between
two adjacent measurement antenna devices is at least half the
wavelength of the antennas. In order to achieved the greatest
possible accuracy with the method according to the invention, the
gap between the conductive tracks of the antennas and the
measurement antennas must be kept as constant as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Other objects and features of the present invention will
become apparent from the following detailed description considered
in connection with the accompanying drawings. It is to be
understood, however, that the drawings are designed as an
illustration only and not as a definition of the limits of the
invention.
[0017] In the drawings, wherein similar reference characters denote
similar elements throughout the several views:
[0018] FIG. 1 shows a measurement system for contact-free testing
of antennas applied to a material web;
[0019] FIG. 2 shows an alternative embodiment of the measurement
system for contact-free testing of antennas; and
[0020] FIG. 3 shows the progression of the high-frequency power
P.sub.ruck reflected by the measurement arrangement.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] Referring now in detail to the drawings and, in particular,
FIG. 1 shows a material web 1 having antennas 2 for RFID labels
applied to it. Antennas 2 are imprinted onto material web 1, which
is configured as a polymer film, as half-wave dipole antennas,
using a conductive ink and an intaglio printing process. Antennas 2
have two central connector ends 3, from which a rectangular
conductive track 4 extends, in each instance. The working frequency
f.sub.A, which can lie at 900 MHZ, for example, is pre-determined
by the total length l of antennas 2, which corresponds to about
half the wavelength. Material web 1 with a plurality of antennas 2
is passed to a measurement device 5, and antennas 2 each are passed
past an assigned measurement antenna arrangement 6 of measurement
device 5 in the region of measurement device 5. In this connection,
measurement antenna arrangement 6 has a separate measurement
antenna 7 for each of conductive tracks 4. Measurement antennas 7
have a high-frequency signal S.sub.mess applied to them by a
transmitter 8, by way of a directional coupler 9; the frequency
f.sub.mess of this signal approximately corresponds to twice the
frequency of the pre-determined working frequency f.sub.A of
antenna 2. Directional coupler 9 emits a first and a second
measurement signal, whereby the first measurement signal is
proportional to the high-frequency power P.sub.vor, which runs to
measurement antenna arrangement 6, and whereby the second
measurement signal is proportional to the high-frequency power
P.sub.ruck, which is reflected by the measurement antenna
arrangement. The front-to-back ratio is determined from the
measurement signals, as a quotient of these two variables, in an
analog divider 10. The value determined for the front-to-back ratio
is subsequently applied to an operation amplifier 11 with threshold
value setting. Depending on whether or not the threshold value was
reached, an evaluation logic 12 determines whether or not
individual antennas 2 each reach pre-determined production
tolerances. For this purpose, at least 50 and preferably at least
100 measurement values are determined by evaluation logic 12 for
each of antennas 2, and subsequently averaged. Antennas 2 that are
recognized as being defective are marked with an imprint by a
printing device 13. However, the position of the defective antennas
2 may also be electronically stored in the memory of a process
control, and subsequently only the antennas 2 that are capable of
functioning with an RFID chip are provided. Or, the defective
antennas 2 may be marked by means of punching, or removed from the
material web 1. The method according to the invention, for
contact-free testing of antennas 2, allows high web speeds of more
than 0.8 m/s and preferably more than 1.6 m/s.
[0022] As shown in FIG. 2, it is possible, particularly in the case
of mass production, to provide several rows 14 of antennas 2 in the
crosswise direction of material web 1, and a separate measurement
antenna arrangement 6 is provided for each of rows 14. In this
connection, adjacent measurement antenna arrangements 6 are
disposed offset by at least half a wavelength (>>1/2) of
antennas 2 in the running direction of material web 1, in order to
prevent reciprocal interference of measurement antenna arrangements
6 with regard to one another. As shown in FIG. 1, each measurement
antenna arrangement 6 has a transmitter 8, a directional coupler 9,
and the related amplifier/evaluation circuit assigned to it.
[0023] FIG. 3 shows the time progression of high-frequency power
P.sub.ruck reflected by measurement antenna arrangement 6, as an
example. When a first antenna 2 approaches, it absorbs part of the
power made available to measurement antenna arrangement 6, thereby
reducing the proportion of the returning power P.sub.ruck. In the
case of resonance between antenna 2 and the frequency offered by
measurement antenna arrangement 6, the amount of the reflected
power P.sub.ruck drops to a minimum. If antenna 2 has a defect, for
example an interruption caused by a scratch, its effective length
is changed and therefore the resonance frequency is also shifted,
and therefore only a small proportion of the high-frequency power
made available by measurement antenna arrangement 6 is absorbed.
The amount of the reflected high-frequency power P.sub.ruck
therefore remains comparatively high. Accordingly, it is possible
to differentiate between antennas 2 that are capable of functioning
and those that are defective by means of setting a suitable
threshold value W. In place of the continuous recording of a
signal, as it is illustrated in FIG. 3, preferably a plurality of
individual measurement values is recorded over a pre-determined
time window for each of antennas 2, within the framework of the
invention, and subsequently averaged. The averaged values are then
compared with a default value. Depending on whether or not the
pre-determined value is exceeded, adherence to the pre-determined
production tolerances is then determined for each antenna 2.
[0024] Accordingly, while only a few embodiments of the present
invention have been shown and described, it is obvious that many
changes and modifications may be made thereunto without departing
from the spirit and scope of the invention.
* * * * *